1. Field of Invention
This invention relates to exhaust gas recirculation (EGR) or crankcase blowby gas recirculation system into an internal combustion engine. More specifically this invention relates to an exhaust gas recirculation system or crankcase blowby system to reduce NOx emission and Hydrocarbon/Particulate emission.
2. Description of Prior Art
With continued tightening of the emission standards for internal combustion engines, particularly NOx, not only has the need to recirculate exhaust gases back into the engine become important, but also has the need to improve EGR technology. The crankcase ventilation gases emit significant amount of particulate and hydrocarbon into the exhaust. Therefore, a means to develop a system to recirculate crankcase gas back into the engine intake system becomes important.
Significant efforts in research and development have been undertaken to re-circulate exhaust gas into the engine. The reason for introducing EGR (exhaust gas re-circulation) in internal combustion engines, is to reduce NOx emission without incurring fuel consumption penalty. The difficulty in introducing EGR in internal combustion engines is that it requires a pumping arrangement or a venturi arrangement. This adds complexity and penalty in fuel consumption. In addition, filling up the air intake system with EGR often leads to poor transient response performance for an internal combustion engine. A similar problem exists for crankcase breathing arrangements for internal combustion engines. The crankcase gases may not be vented to the atmosphere per various Emissions regulations. This leaves the crankcase gas to be vented either to the exhaust stream or be introduced ahead of the compressor inlet in a turbocharged engine arrangement. Venting crankcase gas into the exhaust causes an increase in Particulate matter and Hydrocarbon emission. Also introducing the crankcase gases ahead of the turbocharger causes significant issues with fouling of the compressor and aftercoolers. Introducing the crankcase gas into the air intake system will result in combustion of the crankcase gas in the cylinder. This results in lowering of particulate and hydrocarbon emission.
In general, the exhaust gas pressures in the exhaust manifold for an internal combustion engine are lower than the pressures in the air intake manifold. This provides positive breathing and increased pumping work which results in improved fuel economy.
To deliver EGR to the air intake system, higher exhaust gas pressure is needed, for a system without any pump. Often the turbocharger is resized to obtain higher exhaust gas pressure. This results in loss of fuel economy.
U.S. Pat. No. 5,611,203 to Henderson et al (1997) discloses that creating a venturi in the Intake runner pipe will allow exhaust gas to be drawn. This system will provide EGR supply at higher when there is a sufficient flow of air to create a venturi. However at part load the supply of EGR is limited. To overcome this problem some designs have used a smaller bypass pipe in parallel with valve arrangements. At light load the main air passage is closed and air is diverted through the smaller pipe. This system requires throttling of the Intake runners and complicated valve arrangement for part load EGR delivery. Throttling of the Intake air results in fuel consumption loss and potential for increase in particulate.
Another U.S. Pat. No. 6,044,827 to Pfaffet al (2000) describes a complex exhaust gas recirculation arrangent having valves and ejector placed in the air inlet duct. The supply of exhaust gas to the system will require higher exhaust pressure or a pumping arrangement. Both these features will result in fuel consumption loss and in a complicated system.